Currently there are two main processes by which ceramic matrix composites (“CMCs”) and in particular, melt infiltrated SiC/SiC CMCs are made. One approach is described, for example, in U.S. Pat. Nos. 5,296,311 and 5,840,221, in which a silicon carbide preform is coated by a chemical vapor process, and then subsequently infiltrated with a slurry in a manner similar to slip casting and then allowed to dry. The powder infiltrated preform is then infiltrated with molten Si metal.
A second approach is described in U.S. Pat. No. 6,258,737, in which a melt infiltrated SiC/SiC CMC is made by a pre-preg process in which fiber tows are impregnated with a powder filled binder (also containing preceramic polymers and high carbon char yielding materials) and then formed into shape after the impregnation.
Other powder injection molding methods used in ceramic processing involve heating a binder filled powder to a molten or near molten state and injecting it, under pressure, into a mold or die. This method is usually employed for high throughput operations for making small, complicated parts. This method is typically avoided for manufacturing large components.
Current slurry infiltration methods for preparing CMCs have relatively long cycle times, and provide relatively poor particulate uniformity, poor dimensional control of near-net-shape components, and undesirably rough surfaces. Accordingly, there remains a need for further improvements in these areas. The processes for preparing CMCs described herein may provide reduced cycle times, improved particulate uniformity, increased dimensional control of near-net-shape components, and reduced surface roughness compared to conventional slurry methods. In addition, the methods of the present disclosure may provide increased metal conversion when employed with a melt infiltration process.